Masked target kinescope



INVENTOR ATTORNEY H. B. LAW

Filed June 16, 1951 a. Law WYM: M

.Sm SSG MASKED TARGET KINESCOPE ASIIIJIIIDD Dec. 22, 1953 www@ Patented Dec. 22, 1953 UNITED STA;TES

TN T F l *MASKED'TRGET KNESCOPE Harold BJ Law, Princeton, N. J.,''assignor ltoladio Corporation offAmerica," a corporation `oiSDela- Wale This invention relates to improvements in 4*cathode-ray tubes and has for its principal'object Y` 4to provide Aan improvedl color-television tube' of the masked-target type and one-characterized, yin operationfby its vsubstantial freedom lfrom color-dilution.

There are two varieties of maskedetarget kinescopes; (1) the line-screen varietypexemplied'by German Patent 736,575, and its` French equivalent 866,065 and (2) the dot-srreen` varfiety claimed by Alfred N. Goldsmith incopending f-application, Serial No. 548,239, filed *Augustin '11944, WhichwasV reiiled on July-19,- 1947 fas' Serial ZNo.f'762g1'75, now U. SHPatent"No5-22630542.

'The colorescreen` or target of am'asked-target kinescope comprisesfan vorderly array lof narrow `phosphor-lines, or small phosphor-dots; arranged in `:groups of`A three` colors, usuallyk red, blue-*sand green. The target-assembly includes an @apertured shadow mask through which-electrons #travel in theform of a'beam in tlfieirtransit` to the tri-color screen. The particularfline-iike-'or "dot-like color-phosphor illuminate'datany' given instant is determinedv bythe langle kat whichthe scanning beam (or beams) pass through the apertured shadow mask r"and approaches 'the kscreen. vShould' the beam, kor :electronsderived therefrom, strike a colorephosphor lother than one .toward Which thefbeam was yoriginally di- ;rected, the purityof the color of the .emitted light l is' adversely affected. This. phenomenon is" 'known as ".color-dilution and may `appear to `theiob server-,eitherasa weakening .or .fdilution ofthe .hue of the selected color, or as 'iazhue ofthesame or of another .intensity but 4of.-adifferentf,color .The present inventionis applicabletofmaskedtarget kinescopes of both the lineA-sCreen .and dot-screen varieties and it ispredicatedupon an appreciation of the fact thatcolor-.d'ilution maybe attributed to the presence of strayelectrons within the areacircumscrbed by the ymask andscreen assembly. The stray electrons maylibe either primary or secondary electrons. Or-

dinariiy, the primary-electrons and some'of'the `secondary-electronsv are normally endowed with `a' velocity component substantially parallelto the "axis ofthe beamand were it not-for the presence 'of undesired electricA orelectromagnetic vdeflectying 'forces Vadjacent to the screen `v'area would impinge upon the `.same phosphor A""dotfor line -as the beamv itself.

Accordingly, `the 4"present invention *contemplates, and its construction provides, a targetassembly-Wherein the maskand 'screen-are'electri cally conneetedan'dv operate atY the same potential toprovide a^ field-free space between-'the apertured mask andv` they phosphor screen.

AThe present'invention recognizes that colorvf'dilution may also result from the presence, inthe region ofthe screen,of secondary-electrons of random 1 trajectories. #Such secondary-electrons 4-aref're'leasedA by impact *of the high-velocity pri- "mary-beam or beams upon various partsl of the ftargetassembly. Sinoeelectrons'of random tra- 'jeotories maintain L#their -random `direction of "travel ina eld-freelspace (andA thus eventually impinge upon whichever color-phosphor is in their path), the present linvention provides f a target-assembly rof a `oonstruction,calculated to `minimize the production of secondary-electrons.

More specifically,` fit1 has. been observed. that,. in Ythe mask-edtarget tubes of thevpriorart, the principal sources of disturbing secondary-electrons are (la) the boundary `wallszof Athe masks apertures Lari-ddh) vthe inner surface of the metal frame'within-which the screentand itsrnask are f mounted. The productionof 'secondary-electrons "resulting from. cause (a) is minimized,` in accordance'with; thepresent invention; bythe provision of an:electrically:conductive mask wherein the apertures, `1 through 'which the primary-beam passes, aref'of a-zspecial tapered construction, -`andthe production'. of secondary-electrons result- `ing -l from.' cause (b) s is: minimized, in accordance with; the invention, bythe 'provision of an overzsize'd supporting :frame wherein the inner sur- "faceoftheframeisioutxofthe path of the scanningsbeam.

l''hesinvention;iszz'described in vgreater detail in connection vwith I: the accompanying one sheet yof "drawings wherein:

iFig; 1i is `allongituclinal Asectional View of artriycolor :,niaskedetarget .fkinescope of the ,linescreen variety, embodying the invention;

Fig. zlisiany endfviewof a jig or die used in the -fabrication ;of the wire-like Vtaperedfaperture Tmaskingzelement of Y, the; screeneassembly of Vthe .kineseope:showniinfFig. 1;

,1-Fig.;,3.:isan :enlarged :fragmentary yview of 1 4a dot-like mask and screen assembly/,constructed Lin acoordance-with ,the :principle ofi the .present invention f for :use in"maskedetargenkinescopes of the'idot-screen variety. "The-colorfkinescope shown inFig. yl comprises fanevacua-ted envelope! having a4 main chamber `lin'- theform Vof aL frustum `3:! v'which terminates in -:a--Windowy 5 through which a transparentviewing =screen isvisible. "The other orsmall end ofthe "frustum'fterminates.ina neck portion 9,'--wh-ic'h, in

the instant case, contains a battery of three electron-guns, Il, I3 and I5 arranged 120 apart (delta fashion) about and parallel to the long axis of the tube, as described and claimed by Alfred C. Schroeder in U. Si. Patent 2,595,548, (See also Hannah C. Mocdeys copending application Serial No. 166,416, led February 10, 1950; and since re-nlled on June 24, 1952, as Serial No. 295,255).

The screen 1, here illustrated, is of the linescreen variety shown in German Patent 736,575, previously referred to. It is provided on its rear or target surface with a multiplicity (say 1500, or more) of parallelly disposed phosphor lines R (red), B (blue), G (green) of different coloremissive characteristics, arranged in groups of three. An electron-transparent, light reflecting, film I1, applied over the phosphor lines, covers the entire target surface of the screen 1. The several functions of this conductive film I'I are described later on in this specication.

There is a shadow mask I9 mounted in the path of the electron beams IIg, I3b, i5r and (from the guns II, I3 and I5), in spaced relation with respect to the target surface of the screen l. This mask I9 is made up of a multiplicity of spaced apart wires EI, which extend in a direction parallel to the direction of extension of the phosphor lines R, B and G, and a number of very iine cross-wires 23 (see Fig. 2) which maintain the longitudinal wires 2l in their predetermined spaced relationship. (In the instant case the wires 2| of the mask I9 and the phosphor lines, R, B and G on the screen l' extend in a direction perpendicular to the plane of the drawing. In Fig. 1 the cross wires 2l are concealed by the clamping strips 29 which hold the mask I9 to the base 21 of the supporting frame 25.)

It will be observed upon a close inspection of Fig. 1, that, the mask wires I9 are square (instead of circular) in cross-section and are so mounted, in accordance with the invention, that the long edge of one wire is presented across an intervening space to the long edge of the next adjacent Wire. Thus the entrance and exit of each of the mask apertures may be said to taper outwardly in opposite direction from a central opening whose boundaries are dened by the sharp-edges of the juxtaposed wires. This novel form of mask construction has two advantages:

(1) Irrespective of the instantaneous scanning position of the electron beam (say the red beam I5r), or beams (Iig, tBb) the surfaces of the wires I9 have substantially the same shadowing effect upon the beam. That is to say, the diameter of the beam as it approaches the outer edge of the screen 1, is substantially no smaller than can be expected from the cosine relation.

(2) The secondary-electrons which are released by impact of the scanning-beam upon the inclined plane faces of the square wires are, for the most part, directed away from the aperture, instead of toward it, as though the said faces comprised a mirron Reference has heretofore been made to the electron-transparent, light-reflecting nlm 'l that covers the entire target surface of the screen l. This nlm is preferably constituted of aluminum (applied, by a thermal-evaporation process, in vacuo) and, in addition to its light-reflecting function, has two other functions: (1) it prevents the accumulation of static charge upon the face of the screen and (2) when, as dictated by the 4 present invention, it is connected to the electrically conductive mask I9, it renders the space between the screen 'I and the mask I9 free from any electric neld capable or" deecting the electron beam or beams from their normally straight paths.

Referring still to Fig. 1, the connection between the conductive coating Il, on the screen 'I and the metal mask I9 (which is required to establish a field-free space between said elements of the screen-assembly) is established through a metal frame 25 upon which said parts and I9 are supported. The frame 25 here shown comprises a rectangular base 2l to which the terminals of the masks wires I9 and 2l are aixed, as by welds or solder (not shown), and four clamping strips 29 which urge the conductive film Il on the screen I into contact with the metal base 21 of the frame 25 under the force exerted thereon by screws 3l. The length and breadth dimensions of the inner boundaries of the' metal frame 25 must be substantially greater than the corresponding dimensions of the areas of the mask I9 and screen 'i which lie in the path of the scanning beams Hg, I3b and |51', in order to prevent the beams from striking any part of the frame 25 and releasing disturbing secondary-electrons therefrom.

A lead 33 connects the frame 25, and hence the screen 'I and mask I9 to the second-anode, which is here shown in the form of a conductive coating 35 on the inner surface of the main chamber 3 and neck 5 of the envelope I., The screen assembly itself may be supported in the desired position within the chamber 3 as by means of studs or other suitable means, not shown. The operating potential of the second-anode 35 and of the metalized screen l and its mask I9 may be of the order of from, say, iifteen to twenty kilovolts. Appropriate operating voltages for the other electrode elements `in the tube are'marked on the drawing. Y

Fig. 2 illustrates a preferred method of manufacturing the tapered-aperture line-like masking electrode I9 of Fig. 1. In this drawing, 4I designates a jig or block of metal having a multiplicity of contiguous V-shaped grooves 43, arranged in parallel relation on a surface thereof, for receiving the square wires-2|` The diameter of the grooves 43 is somewhat larger than that of the wires 2I, hence the said wires do not touch each other while in the jig, but are separated Vone from another a distance corresponding to the diameter of the line-like openings in the finished screen. Thisfr spacing between the square wires 2i is maintained by the iine crosswires 23 which are simply stretched across the exposed apices of the former and pressed into said apices as by a hammer or other suitable tool 45. As previously mentioned, the ends of the square wires 2I and the ends of the cross-wires 23 may be affixed to the base 2 of the supporting frame 25 (Figi) by a soldering or welding operation.

Referring now to Figs. 3 and 1. When the invention is applied to a screen and mask 'assembly (5i, 53, Fig. 3) of the dot variety, the desired tapered contour (see Fig. 4) of the dotlike apertures 55 in the mask 53 may be achieved by any of several two-way etching methods. In accordance with one method, the metal blank from which the apertured mask 53r is made, is rst coated on both sides with a photosensitive material (not shown) which hardens when exposed to light. The pattern of the dot-likeaperramasser.

'.'tures 55 is then'applie'd, photographically,"toeach `of the two Iphotosensitiz'ed facesof the .blank,-\.and the unhardened 'dot-like portions .of .therphotosensitive material removed' by Washing. The exposed dot-likesurface areas of the metal are then `edge apex 5l of the two-way vtapered -wallsof eachraperture preferably "(butnot necessarily) lies in the ymid-plane of themetal and theisaid edge and walls are substantially symmetrical about a linee@ drawn perpendicular tothe major .faces of the mask 53. 'I-Ierey as in Fig. 1, the

boundary walls of the apertures are inclined with respect to the axes-of the paths of the beamelectrons irrespective ofthe instantaneousxscan- `ning posit-ions of the beamor. beams. LThelocation of the knife-edges 5l can best be controlled by applying the acid (e. g. ferrie chloride) first to one side of the metal and then to the other by means of one or more spray guns, not shown. When the acid resisting material has been removed, the mask 53 and themetalized phosphordot screen 5l are mounted in a suitable frame (not shown, but which may be similar to the one shown in Fig. l) and are electrically connected together, as symbolically indicated by the lead Si shown in Fig. 3.

Referring now to Fig. 5: In some cathode-ray tubes of the masked-target variety it is advantageous to provide the mask, which is here designated S3, with tapered apertures 65 that are each centered about a median line 6l which is tilted (usually toward the center-of-deflection of the tube) with respect to a line drawn perpendicular to the planes of the major faces of the mask. In such cases it may also be advantageous to make the exit 65m of each aperture slightly larger than its entrance 65e. A mask containing apertures of such a peculiar shape and orientation may be made from a sheet 69 of copper (or other readily etchable metal) by first plating or otherwise coating both sides of the sheet With a thin layer 'H of metal, e. g.

chromium, which is at least slightly more resistant to the etching fluid. The relative size and location of the "entrances 65e and the exits 65x of the apertures 65 may be plotted (e. g. by the lighthouse method described in copending application of Harold B. Law, Serial No. 158,901, now U. S. Patent 2,625,734) and then photographically recorded upon the oppositely located plated faces of the blank.

The etching material is applied as before (e. g. by means of a spray gun), first to one face and then to the other. When the etching liquid has penetrated the surface layers 1l, or one of them, it attacks the less resistant base metall 69 and forms a cavity therein of a diameter larger than that of the hole in the chromium surface-layer. The cavity, thus formed, is converted into a tapered opening, extending through the mask,

by applying the etching material to the other surface of the blank.

One advantage of such an odd-shape maskaperture is that an electron beam in passing therethrough cannot strike the bulbous inner surfaces 85s thereof and release secondaryelectrons. Furthermore, the relatively few secondary-electrons which are released when the beam strikes the knife-like edges surrounding the entrance of each aperture are, for the most part, prevented from emerging from the exit" therei .offbyf reason @off fthe,- small solidfan'gle-isubterrded f by said .exit.

fFrom-the foregoing detailed descriptionz'itiis apparent that' the present inventionv providesian improved 'color-television' tube of .the "maskedltarget varietyiand one characterized,infopera- "ition by its substantial' freedom from fcolordilution.

`What isv claimedis: 1."'In the operationfofa'cathode-rayf'tube of Y the masked-target variety Y containing a .bea'mlvsource of 4electrons'andan apertured electrically'conductive mask through whichy electrons pass in-.the form of a beamte a metallizedviewing screen, the improvement which consistsinfapfzplying. a common :potential to said mask 'fand screen* whereby to.v establish therebetween la "-l'eld free space through which fsaid beam .':passesz'in its transit to saidjscreen.

2. In the operation of a cathode-ray tube of the type comprising a beam-source of electrons,

a second-anode, an apertured electrically conductive target and a metallized viewing screen mounted in the order named within an evacuated envelope, the improvement which consists in applying a common operating potential to said second anode, to said apertured mask and to said viewing screen, whereby to establish within said envelope a field free space through which said beam passes in its transit from said source to said screen.

3. A cathode-ray tube of the masked-target" variety comprising an evacuated envelope containing a beam-source of electrons, a target as,- sembly comprising a metallized viewing screen and an apertured electrically conductive mask through which said beam passes in its transit to said screen, and a conductive connection between said mask and the metallized surface of said screen for applying a common operating potential to said target-assembly and thereby to establish a field free region, within said assembly, through which said beam passes in its said transit to said screen.

4. The invention as set forth in claim 3 and wherein said conductive connection comprises a metal frame upon which said mask and screen are supported.

5. In a cathode-ray color-tube of the kind containing a screen electrode having a target surface consisting effectively of a multiplicity of duplicate groups of sub-elemental image areas of different color-response characteristics, a source of electrons, means for deriving beamelectrons from said source and for projecting said beam-electrons along a plurality of discrete angularly related paths to respective ones of the sub-elemental image areas in each of said groups, and an electrically conductive mask mounted adjacent to said target surface and containing a multiplicity of apertures disposed in a pattern corresponding to the pattern of distribution of said groups of sub-elemental colored image-areas, the improvement which comprises means for obstructing the passage through said apertures of secondary-electrons released by impact of said beam-electrons upon said mask, said means comprising: boundary-Walls for said apertures which are inclined with respect to the axes of the paths of said beam electrons.

6. The invention as set forth in claim 5 wherein the boundary Walls of the apertures in said mask are of tapered contour.

7. The vinvention as set forth in claim 5 and wherein said metallized viewing screen is of the wherein said metallized viewing screen is of the 10 phosphor-dot variety and said apertured mask Y comprises a thin-metal plate-like member containing a multiplicity of apertures having houndary-walls defined, at least in part, by a knifeedge.

9. The invention as set forth in claim 8 and wherein the knife-edge on the boundary walls of said apertures lies substantially in the midplane of said plate-like mask.

10. The invention as set forth in claim 8 and wherein the knife-edge on the boundary-walls of said apertures lies in the plane of a surface of said plate-like mask.

HAROLD B. LAW.

References Cited n the file of this patent UNITED STATES PATENTS Number Name Date 2,248,557 Schlesinger July 8, 1941 2,315,367 Epstein Mai'. 30, 1943 2,529,485 Chew Nov. 14, 1950 2,532,511 Okolicsanyi Dec. 5, 1950 2,567,874 Cage Sept. 11, 1951 2,580,250 Smith Dec. 25, 1951 FOREIGN PATENTS Number Country Date 866,065 France Mar. 31, 1941 

